The present invention relates to a method of input power on/off discrimination for an automatic vehicular transmission system, and more particularly, to a method of input power on/off discrimination based on an output torque of an engine transmitted to an input shaft of an automatic transmission system, in which the result of discrimination is suitably used for the selection of the transmission control logic of the transmission system.
In a conventional transmission control method for an electronically-controlled, automatic vehicular transmission system, the transmission control logic varies depending on the power on/off state of the input torque of the transmission system. In an operation of shift-up from a lower gear ratio mode to a higher one, for example, if the input torque is in a power-on state, a frictional engagement element on the release side is first gradually disengaged so that the rotating speed of an input shaft of the transmission system is temporarily increased to a level a little higher than that of the input shaft speed immediately before the start of transmission control. Thereafter, a frictional engagement element on the connection side is caused to start engagement, and its engaging force is then adjusted. The input shaft speed is gradually reduced toward a rotating speed for the establishment of the higher gear ratio mode, while its changing rate is being adjusted to a predetermined value. When the input shaft speed attains the speed for the higher gear ratio mode, the engagement of the connection-side engagement element is completed.
If the input torque is in the power-off state at the time of the shift-up operation, on the other hand, the release-side frictional engagement element is disengaged on delivery of a shift command, while the connection-side engagement element is kept stand-by at a position just short of an engagement start position until the rotating speed of the input shaft is lowered to a predetermined level. When the input shaft speed is lowered to the predetermined level, the connection-side engagement element is caused to start engagement, and its engaging force is enhanced gradually. The input shaft speed is gradually reduced toward the rotating speed for the establishment of the higher gear ratio mode, while its changing rate is being adjusted to the predetermined value. When the input shaft speed attains the speed for the higher gear ratio mode, the engagement of the connection-side engagement element is completed.
In an operation of shift-down from a higher gear ratio mode to a lower one, moreover, if the input torque is in the power-on state, the release-side frictional engagement element is first gradually disengaged. The rotating speed of the input shaft is gradually increased toward a rotating speed for the establishment of the lower gear ratio mode, while its changing rate is being adjusted to a predetermined value. Since the engine is in its power-on state, the input shaft speed increases by itself if only part of the friction torque of the release-side engagement element is removed. After the input shaft speed is temporarily increased to a level a little higher than that of the speed for the lower gear ratio mode, the connection-side engagement element is caused to start engagement, while keeping this speed level of the input shaft, and its engaging force is increased gradually. Thus, the engagement of the connection-side engagement element is completed.
If the input torque is in the power-off state at the time of the shift-down operation, on the other hand, the release-side frictional engagement element is gradually disengaged so that the rotating speed of the input shaft is temporarily lowered to a level a little lower than that of the input shaft speed immediately before the start of transmission control. Thereafter, the connection-side frictional engagement element is caused to start engagement, and its engaging force is increased gradually. The input shaft speed is gradually increased toward the rotating speed for the establishment of the lower gear ratio mode, while its changing rate is being adjusted to the predetermined value. When the input shaft speed attains a speed level a little lower than the speed for the lower gear ratio mode, the engagement of the connection-side engagement element is completed.
In the aforementioned transmission control method using the transmission control logic varying according to the power on/off state of the input torque, it is essential to discriminate the power on/off state correctly. Conventionally, the discrimination of the power on/off state is based on the polarity, i.e., acceleration or deceleration of the engine output. Such a conventional method is subject to the following drawbacks.
In the discrimination method described above, if the operation is in an up-shift mode, for example, the power-off state is detected even when the engine output is only slightly decelerating or negative. Therefore, the release-side frictional engagement element is disengaged at once, while the connection-side engagement element is kept at the stand-by position until the rotating speed of the input shaft is lowered to the predetermined level. Thus, the input shaft speed cannot readily lower, so that the start of the engagement of the connection-side frictional engagement element is delayed.
In the case of a down-shift mode, moreover, the power-on state is detected even when the engine output is only slightly positive. Accordingly, automatic increase of the rotating speed of the input shaft is awaited, and the input shaft speed cannot readily increase. Thus, the completion of the engagement of the connection-side engagement element is delayed.